BASF 3D Ultrafuse Recycled Polyethylene Terephthalate Fused Filament is a thermoplastic feedstock for Fused Filament Fabrication derived from recycled PET polymer. The product is supplied as 1.75 mm and 2.85 mm nominal diameter filament with a manufacturer-declared diameter tolerance of ±0.05 mm. It is intended for rigid part production where a semi-crystalline aromatic polyester is appropriate and where recycled feedstock introduces batch-dependent molecular weight distribution. The recommended nozzle temperature range is 230–250 °C, and the heated build plate is specified at 70–80 °C on PEI, glass, or textured PET sheet. Pre-drying is mandatory after exposure of the spool to ambient humidity. Functional applications include jigs, fixtures, housings, and short-run production parts for which recycled content is a requirement rather than a cosmetic claim.

Melt processing requires tighter residence-time control than virgin PET because the recycled raw material can contain variable fractions of bottle flake, post-industrial sheet, and extrusion reclaim. In open-frame FFF machines with direct-drive extruders, volumetric throughput should be limited to prevent shear-induced crystallization at the nozzle wall. A heated enclosure is not mandatory, but draft shields reduce warpage on large flat sections. Because the polymer is semi-crystalline, the transition from melt to solid is sharper than in PLA and contributes to reduced stringing when retraction is correctly configured.

What Process Window Governs Reliable Extrusion of Recycled PET Filament?

Extrusion below 230 °C produces insufficient interfacial polymer chain diffusion at the layer boundary. The resulting parts can delaminate under tensile stress perpendicular to the build axis, particularly when layer heights exceed 0.2 mm and cooling fans operate above 30 % speed. Above 250 °C, thermal degradation of the recycled PET accelerates. Observable markers include increased purge smoke, acetic acid odor, and a measurable loss of melt strength. The nozzle temperature should be verified with an external thermocouple probe because thermistor readings in entry-level machines can deviate by ±10 °C. Retraction settings for direct-drive extruders are typically 1–2 mm at 25–35 mm/s. Bowden systems may require 4–6 mm, but feed-path buckling becomes a documented failure mode when retraction exceeds 5 mm with semi-crystalline rPET. Print speeds in the range 30–60 mm/s are supported; lower speeds improve layer fusion but increase heat exposure and the risk of thermal degradation in the melt zone.

After drying to <0.02 % moisture content, room-temperature mechanical properties reported in the manufacturer’s technical literature are summarized below. Values refer to printed specimens conditioned according to ISO 291 at 23 °C and 50 % RH. Direct replacement of design data for injection-molded virgin PET is not appropriate because layer interfaces create anisotropy.

Published data for this specific configuration is limited for dynamic fatigue and creep. Design for long-term load-bearing service should not extrapolate short-term tensile data without additional testing under ISO 899-2 or equivalent. The tabulated values can shift by approximately 10 % between production batches because recycled feedstock molecular weight and comonomer content are less uniform than in prime virgin PET.

Thermal Degradation and Drying Requirements at Relative Humidity Above 60 %

Moisture uptake in PET filament is diffusion-controlled. At 60 % RH and 23 °C, surface moisture can reach 0.2–0.3 wt% within 24 h. When the wet filament is extruded at 250 °C, residual water hydrolyzes ester linkages, reducing intrinsic viscosity and producing brittle parts with low interlayer strength. Pre-drying in a forced-air oven at 60 °C for 4–6 h is the minimum practical treatment. A desiccant dryer with a dew point of −30 °C or lower reduces drying time to 3–4 h. Vacuum drying at 65 °C and 100 mbar is also effective for spools that already show surface haze or microscopic bubbles during extrusion. Ambient relative humidity above 60 % for periods longer than 2 h without a dry box will reintroduce moisture into the filament surface. For continuous production, a feed-path dry box maintained below 15 % RH is the minimum boundary. Failure to maintain dryness commonly appears as small voids on printed walls, reduced transparency in unpigmented parts, and popping at the nozzle.

Thermo-oxidative degradation becomes measurable after repeated extrusion or prolonged residence in the nozzle above 250 °C. The recycled grade may contain trace catalytic residues from washing and grinding operations; these residues can locally accelerate chain scission. Because of this, purge procedures after a failed print should use a fresh purge material, and the hot-end should not be left at processing temperature for more than 30 min without extrusion.

Differences from glycol-modified PET copolymer grades are measurable in both rheology and solid-state properties. The rPET grade lacks the 1,4-cyclohexanedimethanol comonomer that suppresses crystallinity in PETG. Consequently, the rPET melt exhibits a faster crystallization rate on cooling, higher tensile modulus, and lower notched impact strength. In FFF parts printed with similar nozzle settings, rPET typically shows a heat deflection temperature that is 5–10 °C higher than PLA and 2–5 °C lower than typical PETG, depending on part geometry and cooling conditions. Compared with ABS, rPET releases no styrene monomer during normal extrusion and shows lower warpage on large flat sections because the heated bed requirement is lower than ABS and shrinkage is more uniform. However, ABS retains superior impact strength and ketone resistance in many industrial applications. These comparisons are indicative from publicly available datasheets and must be verified on the target printer because fan cooling, layer time, and enclosure temperature alter crystallinity and residual stress.

When Recycled PET Feedstock Varies, Batch-to-Batch Intrinsic Viscosity Shifts

Recycled PET derived from bottle flake or post-industrial sheet can exhibit intrinsic viscosity values from 0.60 dL/g to 0.80 dL/g, depending on source separation and washing history. Solid-state polycondensation may be used by the compounder to raise intrinsic viscosity toward 0.70–0.78 dL/g for filament production. Values below 0.65 dL/g reduce melt strength and can cause unstable filament diameter during extrusion, while values above 0.80 dL/g increase back pressure in hot-end assemblies with short melt zones. For production-scale FFF, batch-to-batch variance should be controlled by incoming melt flow rate testing per ISO 1133-1:2022 at 250 °C/2.16 kg and by recording extruder motor current at constant speed. A documented failure mode in continuous runs is gradual nozzle orifice fouling from titanium dioxide or other pigment residues when colored recycled feeds are used. In brass nozzles, abrasive recycled grades shorten nozzle replacement intervals by 20–30 %. Hardened steel or ruby nozzles are recommended when the feedstock batch contains high recycled pigment loading.

Chemical resistance of rPET follows aromatic polyester behavior. It resists dilute acids, aliphatic hydrocarbons, and many alcohols at room temperature. It is attacked by strong alkalis, ketones, and chlorinated solvents. Stress cracking can occur when printed parts are exposed to hot water or steam above 60 °C for prolonged periods, particularly when rapid cooling has left residual internal stress. Annealing at 110–120 °C for 30–60 min can reduce molded-in stress and increase crystallinity, but the treatment alters dimensions by 0.2–0.5 % and may reduce impact performance. The manufacturer’s datasheet does not position this material as food-contact compliant under FDA 21 CFR or EU Regulation (EC) No 10/2011. Applications requiring direct food contact or long-term medical body contact require separate compliance verification. Published data for this specific configuration is limited for ultraviolet weathering. Black-pigmented or painted versions improve UV resistance, but unpigmented recycled PET will photolytically degrade over extended outdoor exposure without a UV stabilizer.